The present invention relates to a shaft torsional vibration monitor for a multi-mass rotary shaft system, for example, a rotary shaft system of a turbine generator and its prime mover turbine connected thereto.
A shaft torsional vibration is induced in the rotary shaft system and connected turbine when a disturbance is caused by a system fault such as grounding and short circuiting followed by high speed reclosing occurs in a power transmission system to which the turbine generator is connected, or when a disturbance caused by a plant fault in a turbine plant from which the prime mover turbine is supplied with driving power. The shaft torsional vibration thus induced causes fatigue of the rotary shaft. Monitoring of the shaft torsional vibration is very important for the maintenance of the rotary shaft system.
A shaft torsional vibration is induced by a change of an external force applied to the rotary shaft system such as electrical torque applied to the turbine generator rotor and mechanical torque applied to the prime mover turbine rotor.
Under a steady-state operating condition, when both a change in the electrical torque due to a load change in the power transmission system and a change in the mechanical torque due to a turbine driving steam change, gas pressure change or gas flow rate change are small, the electrical torque and the mechanical torque applied to the turbine rotary shaft system balances and no substantial shaft torsional vibration is induced in the turbine rotary shaft system.
Under a non-steady-state operating condition such as a system disturbance caused by grounding or short circuiting fault in the power transmission system and the following high speed reclosing, the change in electrical torque applied to the turbine generator is substantial and the electrical torque and the mechanical torque applied to the turbine rotary shaft system becomes unbalanced and a shaft torsional vibration is induced to the turbine rotary shaft system.
An example of conventional shaft torsional vibration monitors for a turbine generator and its prime mover turbine connected thereto is disclosed in Japanese patent application laid open No. 58-22923 (1983) laid open on Feb. 10, 1983, which includes a plurality of shaft torsion detectors composed of a plurality of turning gears attached to the rotary shaft system and a corresponding number of pick-ups to detect relative shaft torsions, at the respective portions of the rotary shaft system in cooperation with the respective turning gears. The shaft torsional vibration monitor of Japanese patent application laid open No. 58-22923 further detects respective external forces applied to the turbine shaft system and processes both detected signals to determine the shaft torsional vibration induced to the turbine shaft system by solving equations of motion of the turbine shaft system.
Since the rotary shaft system of a turbine generator and its prime mover turbine connected thereto extends as long as several meters, it was necessary to measure shaft torsions at many points on the rotary shaft system. The number of the shaft torsion detectors to be attached was increased which increased the cost of the shaft torsional vibration monitor. Moreover when the shaft torsional vibration monitor must be added to an already installed rotary shaft system such as a turbine generator and its prime mover turbine connected thereto, positions and spaces for the attachment of the shaft torsion detectors of the shaft torsional vibration monitor are extremely limited.